Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $69.66   10.107%   $76.7005   $76.70   $76.70   $76.70  
  Purchase #2 $45.84   7.647%   $49.3454   $49.35   $49.35   $49.30  
  Purchase #3 $164.63   6.758%   $175.7557   $175.76   $175.75   $175.80  
  Purchase #4 $126.40   5.163%   $132.926   $132.93   $132.95   $132.90  
  Purchase #5 $231.57   9.658%   $253.935   $253.94   $253.95   $253.90  
  Purchase #6 $46.41   9.849%   $50.9809   $50.98   $51.00   $51.00  
  Purchase #7 $197.77   12.393%   $222.2796   $222.28   $222.30   $222.30  
  7 purchase totals = $882.28       $961.9231   $961.94   $962.00   $961.90